Western Diamondback Rattlesnake (Crotalus atrox): Facts and Range

Appearance: how to recognize a western diamondback

The western diamondback has a pale ground color that is usually gray, khaki or tan, but can be pinkish, brick red, yellowish or almost white, often matching the local soil. Down its back runs a row of about 23–45 darker brown diamonds or hexagons, each edged with pale scales. The pattern looks dusty and slightly blurred because the scales are speckled, so it is less crisp than that of the eastern diamondback.

The most reliable field mark is the tail. In front of the rattle are usually four to six black rings separated by white or pale gray rings of similar width. This “coon tail” gives the species one of its many nicknames. On each side of the broad, triangular head, two pale diagonal stripes run from the eye toward the mouth.

Like all pit vipers, it has vertical pupils and a heat-sensing pit between each eye and nostril. These pits let it detect the body heat of warm-blooded prey in total darkness. Several other snakes in its range look similar. The Mojave rattlesnake also has a ringed tail, but its black rings are narrower than its white ones, while the black-tailed rattlesnake has a mostly black tail. For a side-by-side guide to its eastern relative, see eastern vs western diamondback.

How big do western diamondbacks get?

Adults are commonly about 1–1.2 m (3.3–4 ft) long. Snakes over 1.5 m (5 ft) are infrequent, those over 1.8 m (6 ft) are very rare, and the largest length considered reliable is about 2.1 m (7 ft). Old stories of 8-foot western diamondbacks are not backed by measured specimens.

Weight increases quickly with length. A medium adult weighs roughly 1.2–2.7 kg (2.6–6 lb), and the heaviest reported snakes reach about 6.7 kg (15 lb). Males grow larger than females once they are mature.

That makes it the second heaviest rattlesnake and one of the largest venomous snakes in North America, behind the eastern diamondback.

Habitat and range

The western diamondback has one of the largest ranges of any rattlesnake. In the United States it lives in central and western Arkansas, most of Oklahoma, much of Texas except the east and the northern panhandle, southern and central New Mexico and Arizona, the southern tip of Nevada and southeastern California. There are also a few records from southern Kansas.

In Mexico it ranges through the northern states, from Sonora and Chihuahua east to Nuevo León and Tamaulipas, and south to about northern Sinaloa, Zacatecas, San Luis Potosí, Hidalgo and northern Veracruz. Isolated populations live farther south in Veracruz and Oaxaca, and the species also occurs on several islands in the Gulf of California, including Tiburón.

It is a generalist that lives from below sea level to about 2,000 m (6,500 ft). Typical habitats include creosote and mesquite flats, desert scrub, dry grassland, rocky canyons and hillsides, coastal plains and beaches in Texas, and the lower edge of pine-oak woodland. It is also one of the rattlesnakes most able to live alongside people. In fast-growing cities such as Phoenix and Tucson, western diamondbacks still turn up in yards, desert washes and the edges of neighborhoods.

Diet and hunting

Western diamondbacks are carnivores that eat mainly small mammals. In one classic study in Texas, mammals made up about 95 percent of the diet by weight. Prey includes kangaroo rats, pocket mice, white-footed mice, woodrats, cotton rats, pocket gophers, ground squirrels, prairie dogs and cottontail rabbits. Large snakes can swallow a full-grown rabbit.

Birds such as quail, ground-nesting songbirds and even burrowing owls are also taken, and young snakes eat many lizards. Unusually for a snake, the western diamondback is also known to scavenge, eating animals that are already dead.

Most hunting is by ambush, at night or in the early morning. The snake coils beside a rodent trail, using scent and its heat-sensing pits to detect prey. It strikes in a fraction of a second, injects venom and lets go, then follows the scent trail to find the dying animal. Its heat pits let it aim accurately even on moonless nights.

Like other large snakes, it can live a long time between meals. In the wild, a rattlesnake may eat only every few weeks, and in one laboratory study western diamondbacks survived more than five months without food by sharply lowering their energy use.

Behavior: rattling, dens and defense

Western diamondbacks are solitary for most of the year. Their daily rhythm depends on temperature: in spring and fall they are active mainly by day and around dusk, while in the heat of summer they switch largely to night activity. On cool evenings they sometimes lie on roads, which hold the day’s heat, and many are killed there. For the full yearly pattern, see when rattlesnakes are most active.

From about late October to early March, most western diamondbacks brumate, a reptile form of winter dormancy, in rock crevices, caves or rodent burrows. In colder parts of the range, such as prairies in Oklahoma, many snakes gather in the same den, sometimes together with other snake species. In warmer areas, shelters are simpler and fewer snakes share them. On warm winter days, they may come out to bask.

The western diamondback has a reputation as one of the more defensive rattlesnakes in the US. Rather than fleeing, it often holds its ground: it raises the front of its body into an S-shaped coil, keeps its head facing the threat and rattles loudly. Its tail-shaker muscles are among the fastest-contracting muscles known in vertebrates. A 2021 study of this species found that it suddenly switches to a higher rattling frequency as a threat comes close. Read more in why rattlesnakes rattle.

During the breeding season, rival males perform “combat dances,” rising up to about 80 cm (31 in) off the ground, wrapping their necks around each other and pushing until one gives up. They do not bite each other.

Reproduction and life cycle

Western diamondbacks can mate in spring after leaving their dens and again in late summer and fall. Females that mate in fall can store sperm until spring. Like all rattlesnakes, the species is viviparous: the young develop inside the mother in thin membranes and are born live.

Births usually take place in late summer, after a gestation of about five and a half to seven months. A litter typically has about 10–20 young, averaging about a dozen to 14, but can reach about 25. Newborns are fully venomous and leave their mother within a few hours to a day, so many die in their first winter from cold, hunger and predators.

At birth, a baby has only a small “prebutton” at the tail tip. It gains its first real rattle segment after its first shed, and a new segment is added with each shed after that. Because snakes shed several times a year and old segments break off, the rattle is not a reliable guide to age; see whether rattles show a rattlesnake’s age. Young snakes reach maturity at about three years old.

Lifespan

The lifespan of wild western diamondbacks is not well documented, because few individuals are followed from birth to death. Many are killed by cars, people or predators long before old age. In captivity, where they are a common zoo species, they often live more than 20 years.

Venom and danger to people

The western diamondback is thought to cause more snakebites than any other snake in the United States, and it is likely responsible for most snakebite deaths in northern Mexico. This is mostly because it is common, large and lives near many people, not because its venom is unusually strong. Drop for drop, its venom is less potent than that of many other rattlesnakes, but its big venom glands deliver a large dose: an average bite yields about 250–350 mg of dried venom.

The venom is mainly hemotoxic, damaging blood vessels, blood cells and tissue. Bites cause severe pain, swelling and bruising and need urgent hospital care. With modern treatment, deaths in the US are rare.

Many bites happen when people try to catch, move or kill a snake, or put hands and feet where they cannot see. Give any rattlesnake plenty of room and let it leave. If someone is bitten, call 911 and seek emergency medical help immediately. For a common myth about young snakes, see are baby rattlesnakes more dangerous?.

Predators and threats

Adult western diamondbacks have several natural predators. Red-tailed hawks, golden and bald eagles, roadrunners, wild turkeys, kingsnakes, coyotes and feral hogs all kill rattlesnakes, especially young ones.

People are the biggest threat. Large numbers are killed on roads and on sight in yards and on ranches. Western diamondbacks are also the main species at the rattlesnake roundups held in Texas and Oklahoma, where snakes are collected from the wild, often by spraying gasoline into their dens, then displayed and killed for meat, skins and entertainment. Gassing dens also harms the many other animals that shelter in them.

Conservation status

The IUCN Red List classifies the western diamondback as Least Concern, with a stable population trend at its last assessment in 2007. Its huge range, wide choice of habitats and tolerance of farmland and suburbs make it one of the most secure rattlesnakes. Some states have limited or banned the gassing of dens, and some roundups have turned into festivals that do not kill snakes.

Relationship with people

The western diamondback is one of the most familiar snakes of the American West and appears in countless films, stories and road-side attractions. Its many local names, such as Texas diamondback, adobe snake and coon tail, show how widely it is known. It is also an important predator of rodents on farms and rangeland. If you live or hike in its range, see snakes in Arizona to learn the harmless species it is often confused with.